Driver error is the cause of many motor vehicle accidents. Sometimes, the driver does not anticipate correctly slippery road conditions, or the driver panics and applies the brakes or the accelerator in a manner that causes the wheels to slip, or uncontrollably slide. Once the wheels start to slide, a driver can quickly loose control of the vehicle. As a result, anti-lock braking (ABS) systems and traction control systems have been developed that detect the onset of wheel slip. These systems control braking and wheel torque to reduce wheel slip. However, unless the driver steers correctly, an accident may still happen. In addition, the effectiveness of traction control and ABS systems is reduced if a vehicle's wheels slide owing to poor grip between the wheels and road, for example, due to ice on a sharp corner.
It is an object of the present invention to provide a dynamic stability control system that can help the driver keep the vehicle on the road when one or more of the wheels starts to slip or slide.
According to the invention, there is provided a motor vehicle comprising a plurality of road engaging wheels, and a dynamic stability control system that includes a means for deducing the position and orientation of the vehicle with respect to a roadway on which the vehicle travels, a path prediction system for predicting the trajectory of the motor vehicle with respect to the roadway and for identifying when the predicted trajectory would place the vehicle in danger, and a wheel slip detection system for detecting loss of traction of one or more of the wheels, wherein the dynamic stability control system is arranged to predict the trajectory of the vehicle, determine whether the predicted trajectory would place the vehicle in danger, and, if loss of wheel traction is detected when the predicted trajectory would place the vehicle in danger, to alter the predicted trajectory in such a way that the identified danger is reduced or eliminated.
The dynamic stability control system may alter the trajectory by altering the degree of braking applied to at least one of the wheels of the vehicle by the vehicle braking system, or by altering the level of drive torque applied to at least one of the wheels by whatever motive means the vehicle includes. This may include, for example, a controllable differential which can vary the distribution of drive torque between the two sides of the vehicle. Systems using control of the magnitude and distribution of braking and/or driving torque between the wheels have the advantage that the trajectory of the vehicle can be controlled without the need for expensive and complex active steering or steer by wire systems. However, where the vehicle includes a steer by wire, active steering, or electric power assisted steering system, the vehicle trajectory can be altered using the steering system. In any event, because the system only starts to alter the vehicle's trajectory when loss of traction is detected, for most of the time the driver retains direct control over the vehicle's trajectory. In the case of steer by wire, the steering can be controlled so as to follow the steering angle requested by the driver using the steering wheel when loss of traction is not detected. The steering then only becomes truly active during loss of traction.
The motive means may include any type of motor, such as an internal combustion engine or an electric motor.
The dimensions and shape of the roadway, including the width of the roadway, the radius of curves, the location of lanes, hard shoulders, crash barriers and fixed obstacles may all be measured as the vehicle travels on the road. For example, a forward-looking radar or machine vision system may include processing means by which any of the above factors may be determined. The position of a lane in the roadway may be deduced over time from the course the vehicle travels and the measured dimensions and shape of the road. From this, the position and orientation of a vehicle with respect to the roadway may be deduced. In practice, however, it may be difficult to use radar or machine vision to detect and measure unambiguously various features in a continuous manner as the vehicle travels down the roadway, particularly if it is desired to achieve a precision high enough to enable a good estimate of danger in the event of wheel slip. In many cases, the difference between a safe vehicle trajectory and a dangerous vehicle trajectory may be a difference in trajectory of about 1 m or less. Preferably, the predicted vehicle trajectory is accurate to within ±0.1 m of the actual trajectory.
Another approach to predicting the vehicle trajectory with respect to a roadway involves a priori knowledge of roadway dimensions and shape combined with means by which the position and orientation of the vehicle can be accurately estimated, for example using internal vehicle movement sensors. For example, road speed can be measured directly from wheel speed sensors as part of a known anti-lock braking system (ABS). The vehicle may also have a number of accelerometers or yaw rate sensors, by which changes in vehicle orientation with respect to a co-ordinate system can be deduced. In general, the shape and characteristics of a roadway can be measured beforehand and stored in the vehicle for future use. For example, such stored data may be generated by a road mapping agency or company, or by the vehicle itself on a previous run over a particular route. In the latter case, numerous vehicles may upload data, for example by radio or cell phone link, to a central repository of such vehicle generated road map data, from which individual vehicles may then similarly download particular road map data.
Therefore, the means for deducing the position and orientation of the vehicle with respect to the roadway may include a memory means that stores road layout data for a geographical area in which the vehicle travels.